In a V-block refractometer which is an example of a refractometer, a sample is placed in a V-shaped groove formed on a V-block prism, and the sample is irradiated with measurement light through the V-block prism. In this way, a refractive index of the sample may be measured by detecting measurement light penetrating the sample using a detector (for example, see Patent Document 1 below).
In this type of refractometer, a part of measurement light guided to the detector by penetrating the sample is separated by, for example, a beam splitter and guided to an eyepiece section (not illustrated). At the time of adjusting a position of the V-block prism, etc., an operator may perform an operation while visually observing a state of measurement light by looking into the apparatus from the eyepiece section.
However, in such a refractometer, the eyepiece section is covered with a cap during measurement to prevent light outside the apparatus from entering from the eyepiece section during measurement and influencing a detection result by the detector. For this reason, there is a problem that an actual state of measurement light may not be observed during measurement.
In this regard, there has been a considered configuration in which a camera is attached to the eyepiece section, incidence of light outside the apparatus from the eyepiece section is prevented, and measurement light is captured by the camera in the eyepiece section, thereby allowing observation of the image captured by the camera during measurement. Patent Document 2 below proposes a configuration in which a graph showing detected intensity of measurement light detected by a detector and an image of measurement light captured by a camera are displayed on one display screen in real time.
A refractive index of a sample is automatically calculated from a peak value of detected intensity of measurement light detected by a detector. However, for example, when the sample is a resin or a liquid, a refractive index of the sample becomes nonuniform in many cases. In such a case, when the refractometer to which the camera is attached is used, the operator may determine whether a state of the sample or a measurement result is acceptable by checking a shape of the graph and the image of the camera.
Patent Document 1: International Publication No. 2015/001650
Patent Document 2: International Publication No. 2014/207809